thanks! I guess my intuition was that 3 layers of nuts should allow for a good-enough heat distribution. I'll do an experiment :)
– OferJul 7 '17 at 9:00

You're more likely to have them go evenly in 1 layer than in multiple layers, but depending on your oven, you'll still need to stir them or rotate the pan. My oven, for example, has terrible hot spots which makes toasting things like coconut especially a nightmare.
– BatmanJul 7 '17 at 21:13

You can roast nuts in the oven in a thicker layer, however you'll need to open the door often to stir them around to make sure they roast evenly and it ends up being more work than roasting them in batches.